The configuration of a typical Bluetooth receiver is introduced in FIG. 1. Referring to FIG. 1, the Bluetooth receiver includes a front-end circuit 110 configured to obtain a baseband signal by demodulating a received signal, a filter 120 configured to selectively pass a desired channel therethrough and remove an undesired channel, and a recovery circuit 130 configured to convert the received baseband signal in the frequency domain into time domain symbols.
The front-end circuit 110 of the Bluetooth receiver obtains a baseband signal by controlling the magnitude of the received signal, and obtains samples by digitizing the obtained baseband signal. Since the magnitude of the received signal may vary over a wide range while passing through a wireless channel, the front-end circuit 110 attempts to maintain the magnitude of the baseband signal within an allowable range by performing automatic gain control (AGC). The automatic gain control may be performed in a manner that avoids the clipping of an analog-digital converter (ADC) that is used for the saturation of a receiver circuit and the digitization of a baseband signal.
FIG. 2 is a diagram showing a typical packet of Bluetooth Smart. Referring to FIG. 2, the packet of Bluetooth Smart includes a preamble interval 210, an access address interval 220, a protocol data unit (PDU) interval 230, and a CRC interval 240. Since a Bluetooth receiver must identify an address during the access address interval 220 and must identify and process data during the PDU interval 230, preparation for the identification of the address and the data must be completed during the preamble interval 210. Accordingly, there is a time limitation in that operations, such as automatic gain control, frequency offset compensation, timing compensation, etc., must be performed within a preamble interval of Bluetooth or Bluetooth Smart in the front-end circuit 110 of the Bluetooth receiver.
An example of preceding technology for rapidly performing automatic gain control during a preamble interval in a Bluetooth receiver is disclosed in U.S. Pat. No. 8,903,203 entitled “Adaptive Bluetooth Receiver and Method.”
The preceding technology can perform compensation based on automatic gain control and DC offset calculation during a preamble interval having a setting similar to that of FIG. 2. The preceding technology performs primary automatic gain control in a fast Received Signal Strength Indicator (RSSI) detector, estimates a DC offset by calculating the DC average value of a preamble, and performs detailed automatic gain control in a slow RSSI detector.
The preceding technology can determine whether the result of the operation of the fast RSSI detector is larger than a threshold value THD in the primary automatic gain control process using the result of the operation of the fast RSSI detector, and then can increase or decrease gain. However, this operation requires the estimation of the range of strength of a signal at an initial step, and thus a disadvantage arises in that it is difficult to deal with a Bluetooth Smart signal in which the dynamic range of a received signal is about 100 dB.
That is, the preceding technology cannot perform sufficient automatic gain control for a Bluetooth Smart signal, in which the dynamic range thereof is about 100 dB, during a preamble interval, and thus there is a need for a means for overcoming this problem.